* @return the n-folded data of the specified length
     */
    public static byte[] expandNFold(byte[] data, int outlen) {
        int lcm = lcm(outlen, data.length);
        byte[] buf = new byte[outlen];
        int carry = 0;
        for (int i = lcm - 1; i >= 0; i--) {
            carry = carry_add(data, buf, carry, i);
        }

        if (carry != 0) {